Roll formed metal profile of thin sheet

ABSTRACT

A roll-shaped thin metal profile is made from a flat steel blank and has a required rupture limit higher than that one of the flat steel blank. The roll-shaped thin metal profile has a width selected in response to the required rupture limit.

[0001] The present invention relates to a roll-shaped thin plate metal profile, the strength and/or shaping properties of which vary partially in its longitudinal direction.

[0002] The material content of roll-shaped profiles available today does, in its longitudinal direction, exhibit constant strength and/or shaping properties. Accordingly, these prior art profiles have a strength, which is constant along all of its length, which per se is not a disadvantage in most applications. However, in the fields where e.g. the weight of the profiles may be of importance, e.g. within the aircraft and motor car industry, this is a drawback, since it is not necessary for the profile to have the same strength and shaping properties along all of its length. Instead, in those cases it would be enough if the profile had a sufficient strength corresponding to the calculated load or stress. It has also proved difficult, when the roll-shaped profiles consist of ultrahigh strength steel, later to carry out some form of shaping, e.g. embossing on the surface of the profile, bending it or carrying out a subsequent punching of the material.

[0003] The object of the present invention is to provide a roll-shaped metal profile of the kind mentioned above, at which the disadvantages enumerated above have been eliminated. The features characterizing the invention are set out in the claims.

[0004] Thanks to the invention there has now been provided a roll-shaped thin plate metal profile, which in an excellent manner fulfils its purpose and, in addition thereto, at the same time is both simple and cheap to manufacture. By use of the profile according to the invention it becomes possible to match the width of the flat blank, from which the profile is made, to the relevant stress. In this way the weight can be reduced with maintained bending stress strength. The profile according to the invention can be manufactured both as I-beams and tubes having a circular or square cross-section. In those load cases, when the profile is clamped at its one end and the force is applied at the other end, the greater material area is at the clamped end. If the profile is loaded between two support points, the greater material cross-sectional area should be at the center. In order to facilitate a finishing shaping or machining of the profile either the blank, from which the profile is made, or the finished profile is exposed to a partial heating to above 300° C., which produces a remaining reduction of the rupture and tensile limits of the profile material.

[0005] Some chosen preferred embodiments of the invention will now be described with reference to the drawing, in which

[0006]FIG. 1 shows a profile blank having varying width and used to produce a profile in the shape of a tube according to the invention,

[0007]FIG. 2 shows a completed tube or post according to the invention made from the profile blank in FIG. 1, four different cross-sections through the tube being illustrated,

[0008]FIG. 3 shows an alternative embodiment of a blank for a profile constituted by an I-beam,

[0009]FIG. 4 shows, at four different cross-sections, a roll-shaped profile in the form of an I-beam made from the blank in FIG. 3,

[0010]FIG. 5 shows a cross-section through a profile, which according to the invention has been given a tubular shape, and

[0011]FIG. 6 shows in a compacted manner the roll-forming steps starting from a blank exhibiting a varying width and generating the profile shown in FIG. 5.

[0012] As appears more in detail from the embodiment of the invention illustrated in FIGS. 1 and 2, one has here started from a flat blank 1 of varying width, which is intended to match the strength properties desired in the completed profile 2, which is in detail and in cross-section illustrated in FIG. 2. This profile 2 is intended to form a post or a strut for e.g. a vehicle and the flat blank 1 of the profile 2 does at its base 3 have a width greater than that at its top portion 4. In this way the completed post or tube will have its greatest strength at the lower portion, or mounting portion, where the stress is highest, in the case that the post or strut is to be used to support e.g. a road sign or as a strut in a vehicle or the like. The upper portion 4 of the profile 2, where the stresses are not so high, has been made weaker. In this way there has been provided a profile 2, which both has a lower weight and where the material consumption is lower compared with conventional profiles having a uniform cross-sectional profile.

[0013]FIGS. 3 and 4 illustrate an alternative embodiment relating to a blank 7 and its profile 5 forming an I-beam to be used in the back support of a motor car chair, in which the highest stress in the profile 5 is at the mounting end 6. FIGS. 5 and 6 show an alternative embodiment, according to which the blank 11 for the profile 10 is tubular and exhibits inwardly folded portions 8, 9, the extension of which in the transverse direction of the profile 10 varies in the longitudinal direction. Consequently, also in this embodiment material is conserved, the strength of the profile 5, 10 being highest in the places where it is most exposed to forces. In the above-mentioned tubular profiles 2, 5, 10 having a non-linear material content one has thus attained a lower weight completely or partly maintaining the strength against bending stresses. When the profile 2, 5, 10 is manufactured it is shaped starting from a flat metallic blank 1, 7, 11 in long, rolled strips, which are cut before or after having been given a roll profile. The profile 2, 5, 10 can also be manufactured from prestamped blanks of formate sheet. If the roll profiling starts from a strip, the width thereof can be varied in a non-linear manner in the way that material is separated by cutting, stamping, nibbling or by different shearing methods. If the roll profiling starts from blanks, the width thereof can be varied according to the methods described above.

[0014] Roll-shaped profiles 2, 5, 10 of an ultrahigh stress steel having a tensile limit above e.g. 700 N/mm² must partially be given a greater plastic deformation than that which the starting material tolerates without rupturing. According to the invention this can be achieved in the way that the blank, or the completed profile, is partially heated to above 300° C., resulting in a remaining reduction of the rupture and tensile limits, which facilitates a subsequent shaping. This shaping may consist in e.g. a bending of the profile or in a punching or embossment of the material, which process is then facilitated. The heating can be carried out according to different methods, e.g. induction heating, laser heating or with the use of hot dies. In certain cases it could also be suitable to heat portions of the completed profile 2, 5, 10 in order to attain a reduction of the rupture and tensile limits in preparation of a subsequent treatment.

[0015] In the motor car manufacturing industry the thickness difference between plates to be welded together butt to butt must not be too great. The thickness ratio 1:2 is suitable. However, in the use of sheets of a high-stress material having a tensile limit exceeding 700 N/mm², the critical parameter is not the thickness but rather the strength of the material. The reason for this is that such sheets have a strength about 6 times that of an ordinary, soft sheet. To get a smooth transition between the materials one can heat the ultrahigh strength steel sheet at the transition to the ordinary, soft sheet to a temperature above 300° C. in locations along all of the edge secured to the soft sheet. Accordingly, this partial heating is used on the one hand to facilitate a subsequent treatment of the ultrahigh strength steel and, on the other, to achieve a soft transition in the weld joint between it and an ordinary, soft sheet. If this treatment is not carried out the weld joint will rupture due to the different strength properties of the two materials.

[0016] A partial heating of the ultrahigh strength sheet is also carried out in such portions of the sheet which shall be adapted to serve as deformation zones in e.g. vehicles. This is done to diminish the damages, which otherwise would occur upon a collision, namely if certain exposed portions of a vehicle are more easily deformed than other portions also consisting of that ultrahigh strength material. 

1. A roll-shaped thin sheet metal profile with partially along its longitudinal direction varying strength and/or shaping properties, characterized in that the flat blank (1, 7, 11) creating the profile (2, 5, 10) is constituted by an ultrahigh strength steel having a high tensile limit, the width of the blank being selected to match a relevant strength property.
 2. A metal profile according to claim 1, characterized in that its tensile strength amounts to above 700 N/mm².
 3. A metal profile according to claim 1, characterized in that the blank (1, 7, 11) or the completed profile (2, 5, 10) has been exposed to a heat treatment by partial heating to above 300° C. within selected portions of the sheet in order to produce a remaining reduction of the rupture and tensile limits in order to facilitate a subsequent shaping or to produce deformation zones. 